RF transmitter

1. A radio frequency, RF, transmitter, comprising: a digitally controlled oscillator, DCO, configured to generate an RF signal; and digital modulation circuitry connected to the DCO for modulation of the RF signal, and driven by an RF clock signal derived from the RF signal, wherein the digital modulation circuitry is configured to apply a compensation for modulation jitter due to the digital modulation circuitry being driven by the RF clock signal and a compensation for DCO non-linearity, and wherein the compensation for modulation jitter and the compensation for DCO non-linearity are applied to a capacitor control of the DCO.

2. A radio frequency transmitter according to claim 1 , wherein the compensation for modulation jitter can be written as a frequency compensation factor α = F R ⁢ F F R ⁢ F - F c ⁢ o ⁢ n ⁢ trol , wherein F RF is a nominal RF frequency for the DCO and F control is a deviation from the nominal RF frequency to which the DCO is modulated.

3. A radio frequency transmitter according to claim 2 , wherein the compensation for modulation jitter and the compensation for DCO non-linearity are applied in a single step.

4. A radio frequency transmitter according to claim 3 , wherein the DCO non-linearity comprises an LC non-linearity.

5. A radio frequency transmitter according to claim 3 , wherein the compensation for modulation jitter and the compensation for DCO non-linearity can be written as a capacitance compensation factor c ⁡ ( m ) = 1 - 4 ⁢ π 2 ⁢ L ⁢ C ⁡ ( F R ⁢ F + α ⁡ ( m ) ⁢ m ⁢ d ⁢ F ) 2 4 ⁢ π 2 ⁢ L ⁢ d ⁢ C ⁢ m ⁡ ( F R ⁢ F + α ⁡ ( m ) ⁢ m ⁢ d ⁢ F ) 2 , wherein α ⁡ ( m ) = F R ⁢ F F R ⁢ F - m ⁢ d ⁢ F , wherein F RF is a nominal RF frequency for the DCO, m represents a number of connected capacitors, L is a DCO LC circuit inductance, C is a DCO LC circuit capacitance, dC is a switchably connectable capacitance, and dF is a fixed frequency step.

6. A radio frequency transmitter according to claim 2 , wherein the DCO non-linearity comprises an LC non-linearity.

7. A radio frequency transmitter according to claim 2 , wherein the capacitor control is a capacitor control code of the DCO.

8. A radio frequency transmitter according to claim 1 , wherein the compensation for modulation jitter and the compensation for DCO non-linearity are applied in a single step.

9. A radio frequency transmitter according to claim 8 , wherein the DCO non-linearity comprises an LC non-linearity.

10. A radio frequency transmitter according to claim 8 , wherein the compensation for modulation jitter and the compensation for DCO non-linearity can be written as a capacitance compensation factor c ⁡ ( m ) = 1 - 4 ⁢ π 2 ⁢ L ⁢ C ⁡ ( F R ⁢ F + α ⁡ ( m ) ⁢ m ⁢ d ⁢ F ) 2 4 ⁢ π 2 ⁢ L ⁢ d ⁢ C ⁢ m ⁡ ( F R ⁢ F + α ⁡ ( m ) ⁢ m ⁢ d ⁢ F ) 2 , wherein α ⁡ ( m ) = F R ⁢ F F R ⁢ F - m ⁢ d ⁢ F , wherein F RF is a nominal RF frequency for the DCO, m represents a number of connected capacitors, L is a DCO LC circuit inductance, C is a DCO LC circuit capacitance, dC is a switchably connectable capacitance, and dF is a fixed frequency step.

11. A radio frequency transmitter according to claim 1 , wherein the DCO non-linearity comprises an LC non-linearity.

12. A radio frequency transmitter according to claim 11 , wherein the compensation for modulation jitter and the compensation for DCO non-linearity can be written as a capacitance compensation factor c ⁡ ( m ) = 1 - 4 ⁢ π 2 ⁢ L ⁢ C ⁡ ( F R ⁢ F + α ⁡ ( m ) ⁢ m ⁢ d ⁢ F ) 2 4 ⁢ π 2 ⁢ L ⁢ d ⁢ C ⁢ m ⁡ ( F R ⁢ F + α ⁡ ( m ) ⁢ m ⁢ d ⁢ F ) 2 , wherein α ⁡ ( m ) = F R ⁢ F F R ⁢ F - m ⁢ d ⁢ F , wherein F RF is a nominal RF frequency for the DCO, m represents a number of connected capacitors, L is a DCO LC circuit inductance, C is a DCO LC circuit capacitance, dC is a switchably connectable capacitance, and dF is a fixed frequency step.

13. A radio frequency transmitter according to claim 12 , wherein the compensation for modulation jitter and the compensation for DCO non-linearity are applied in a single step.

14. A radio frequency transmitter according to claim 13 , wherein the DCO non-linearity comprises an LC non-linearity.

15. A radio frequency transmitter according to claim 14 , wherein the compensation for modulation jitter and the compensation for DCO non-linearity can be written as a capacitance compensation factor c ⁡ ( m ) = 1 - 4 ⁢ π 2 ⁢ L ⁢ C ⁡ ( F R ⁢ F + α ⁡ ( m ) ⁢ m ⁢ d ⁢ F ) 2 4 ⁢ π 2 ⁢ L ⁢ d ⁢ C ⁢ m ⁡ ( F R ⁢ F + α ⁡ ( m ) ⁢ m ⁢ d ⁢ F ) 2 , wherein α ⁡ ( m ) = F R ⁢ F F R ⁢ F - m ⁢ d ⁢ F , wherein F RF is a nominal RF frequency for the DCO, m represents a number of connected capacitors, L is a DCO LC circuit inductance, C is a DCO LC circuit capacitance, dC is a switchably connectable capacitance, and dF is a fixed frequency step.

16. A radio frequency transmitter according to claim 13 , wherein the compensation for modulation jitter and the compensation for DCO non-linearity can be written as a capacitance compensation factor c ⁡ ( m ) = 1 - 4 ⁢ π 2 ⁢ L ⁢ C ⁡ ( F R ⁢ F + α ⁡ ( m ) ⁢ m ⁢ d ⁢ F ) 2 4 ⁢ π 2 ⁢ L ⁢ d ⁢ C ⁢ m ⁡ ( F R ⁢ F + α ⁡ ( m ) ⁢ m ⁢ d ⁢ F ) 2 , wherein α ⁡ ( m ) = F R ⁢ F F R ⁢ F - m ⁢ d ⁢ F , wherein F RF is a nominal RF frequency for the DCO, m represents a number of connected capacitors, L is a DCO LC circuit inductance, C is a DCO LC circuit capacitance, dC is a switchably connectable capacitance, and dF is a fixed frequency step.

17. A radio frequency transmitter according to claim 1 , wherein the digital modulation circuitry is configured for polar modulation of the RF signal.

18. A radio frequency transmitter according to claim 1 , wherein the digital modulation circuitry is configured to oversample the RF signal to be modulated.

19. A radio frequency transmitter according to claim 1 , wherein the radio frequency transmitter includes a wideband polar orthogonal frequency division multiplex (OFDM) radio frequency transmitter.

20. A radio frequency transmitter according to claim 1 , wherein the digital modulation circuitry includes a frequency linearization module to apply the compensation for modulation jitter due to the digital modulation circuitry being driven by the RF clock signal and the compensation for DCO non-linearity.

21. A radio frequency transmitter according to claim 1 , wherein the compensation for DCO non-linearity and the compensation for modulation jitter work in opposite directions.

22. A radio frequency transmitter according to claim 1 , wherein the compensation for modulation jitter and the compensation for DCO non-linearity are applied in a sequence.

23. A method of generating a digitally-modulated radio frequency, RF, signal, using an RF transmitter comprising: a digitally controlled oscillator, DCO; and digital modulation circuitry connected to the DCO, the method comprising: generating, at the DCO, an RF signal; driving the digital modulation circuitry by an RF clock signal derived from the RF signal; inputting, at the digital modulation circuitry, symbols for modulation; applying, at the digital modulation circuitry, a compensation for modulation jitter due to the digital modulation circuitry being driven by the RF clock signal and a compensation for DCO non-linearity; and modulating the RF signal as controlled by the digital modulation circuitry, wherein the compensation for modulation jitter and the compensation for DCO non-linearity are applied to a capacitor control of the DCO.